To Florida teenager Kiera Wilmot, it was a simple experiment in preparation for her school's science fair, mixing common household chemicals in a small plastic bottle to see how they would react.

Witnesses say the bottle popped "like a firecracker", harmlessly blowing off the lid and creating a small amount of smoke.

But to staff at Bartow High School, police officers and an assistant state attorney with a zero-tolerance attitude, her actions were much more serious.

The unsupervised experiment on school grounds ended with Wilmot, 16, led away to a juvenile detention facility in handcuffs, expelled and charged as an adult with felony possession of a weapon and making or discharging a destructive device, with a possible penalty of up to 20 years in jail.

The episode has pitted campaigners for a common-sense approach to school discipline against an unrepentant school district that insists it is just following rules, warning parents to advise their children that there will always be "consequences to actions".

"This is totally insane," Dr Kathleen Nolan, a lecturer in teacher preparation at Princeton University and author of Police in the Hallways: Discipline in an Urban High School told the Guardian.

"This young woman faces expulsion, felony charges and a criminal record because of what appears to be misguided curiosity. These zero tolerance laws have put into place a mindlessness where individuals no longer think through these kind of situations and use their discretion."

According to Wilmot's arrest report, the school's assistant principal Dan Durham said he was walking around the campus before classes began and heard "an explosion". He said he saw Wilmot near the area and she told him she was conducting an experiment for the science fair.

He called police when the girl's science teacher told him that it was not part of any class work.

In the report, officer Gregory Rhoden of the Bartow police department said Wilmot brought a plastic water bottle from home, in which she mixed some toilet bowl cleaner and aluminum foil.

"Wilmot advised she did not know what would happen when she mixed the ingredients. She thought it would just cause some smoke," Rhoden said."Wilmot advised in no way was she trying to hurt anyone or cause a disruption at school."

Ron Pritchard, the school's principal, confirmed that nobody was hurt and no school property was damaged. He told Tampa Bay TV station WTSP that Wilmot was "a good kid" and a model student.

"She made a bad choice. Honestly, I don't think she meant to ever hurt anyone. She wanted to see what would happen and was shocked by what it did. She has never been in trouble before. Ever," he said.

That cut little ice with Polk County's assistant state attorney Tammy Glotfelty, who advised Rhoden to charge the girl with the two felony offences. Her office told the Guardian on Thursday: "The case is under investigation. We have no comment at this time."

The Polk County school board, meanwhile, issued a statement announcing it was disappointed by Wilmot's "bad choice".

"The incident was a serious breach of conduct. In order to maintain a safe and orderly learning environment, we simply must uphold our code of conduct rules. We urge our parents to join us in conveying the message that there are consequences to actions. We will not compromise the safety and security of our students and staff," the statement said.

Wilmot, whose family has made no comment, now faces the likelihood of having to complete her high school studies at home. Her supporters have launched an online petition at change.org calling for the "unjust" charges to be dropped, which had attracted more than 18,000 signatures by lunchtime Thursday.

"Given that this case is so high profile, the hope is that somebody will intervene and get something going in the right direction," Dr Nolan said."Unfortunately there are so many young people like her whose lives have been turned in a different direction because of an overreaction. I've heard so many teacher and administrators lament, 'There's nothing I can do.'"